Alcohol abuse is a significant global health problem. Chronic alcohol drinking can induce alcoholic liver disease, which ranges from steatosis (fatty liver) to steatohepatitis, fibrosis and cirrhosis. About 90% of heavy alcohol drinkers develop alcoholic fatty livers (AFL), an onset of alcoholic liver disease. Recently, we found that CYP2A5 is induced by chronic ethanol feeding and CYP2A6 is elevated in alcoholic patients. CYP2A5/6 is a major nicotine metabolic enzyme. Alcohol and tobacco are frequently co-abused and tobacco smoke can increase alcoholic fatty liver. Our preliminary results indicate that nicotine can enhance AFL and hypertriglyceridemia (HTG), which was observed in WT mice but not in cyp2a5-/- mice. In AIM 1 we will reintroduce CYP2A5 back to cyp2a5-/- mice via AAV8 to confirm the essential role of CYP2A5 in the nicotine-enhanced AFL and HTG and apply cotinine and antioxidants to examine the role of CYP2A5-produced nicotine metabolites and oxidative stress in the nicotine-enhanced AFL and HTG. FGF21 is a novel metabolic regulator highly expressed in liver. Liver FGF21 is regulated by PPAR?. Constitutive elevation of PPAR?-FGF21 in liver was observed in cyp2a5-/- mice. Ethanol-induced HTG, which was observed in ppar?-/- mice but not in WT mice, can be blocked by rFGF21. FGF21 modulates cellular activity through FGF receptor 1 (FR1), which is mainly expressed in adipose tissues. Liver FGF21 can be released into blood to act in an endocrine manner. FGF21 can stimulate adipocytes to secret adiponectin, which in turn acts on the liver to ameliorate AFL. In AIM 2 we will examine the role of a PPAR?-FGF21 axis in the nicotine- enhanced AFL and HTG by applying PPAR? and FGF21, liver-specific FGF21 knockout mice and PPAR? specific agonist WY-14,643. In AIM 3 adipose-specific FR1 knockout mice and adiponectin knockout mice will be applied to evaluate if PPAR?-regulated liver FGF21 exerts its action in adipose tissue through adiponectin i.e. the PPAR?-FGF21-adiponectin to regulate nicotine-enhanced AFL and HTG. At last, adiponectin and CYP2A5 double knockout mice will be applied to investigate the role of adiponectin in the observation that nicotine-enhanced AFL and HTG was observed in WT mice but not in cyp2a5-/- mice.